Extereme 3 gen3

hi guys
i have problem with windows experience index
before i have msi z68 mainboard
but my mainboard have problem
and now i have asrock extereme 3 gen3
my windowse experience index is same just my ram change
before my ram was : 7.8
but now is :5.5
why ?
i changed my ram bus to 1600 same same msi , and run assessment again , but nothing happened ?
tnx if some one can help me